/*
 * Copyright (c) 2004-2022, University of Oslo
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * 3. Neither the name of the copyright holder nor the names of its contributors 
 * may be used to endorse or promote products derived from this software without
 * specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.hisp.dhis.commons.util;

import java.util.ArrayList;
import java.util.List;

/**
 * Class which represents a range between two indexes.
 *
 * @author Lars Helge Overland
 */
public class PageRange {
  /** The current from index. */
  private int fromIndex = 0;

  /** The current to index. */
  private int toIndex = 0;

  /** Total number of values. */
  private int values;

  /** Size of pages. */
  private int pageSize;

  protected PageRange() {}

  public PageRange(int values) {
    this.values = values;
  }

  /**
   * Sets page size.
   *
   * @param pageSize the page size.
   * @return this object.
   */
  public PageRange setPageSize(int pageSize) {
    this.pageSize = pageSize;
    return this;
  }

  /**
   * Sets number of pages.
   *
   * @param pages the number of pages.
   * @return this object.
   */
  public PageRange setPages(int pages) {
    this.pageSize = (int) Math.ceil((double) values / pages);
    return this;
  }

  /**
   * Moves the range to the next page. Returns true if the range has another page, false if not.
   *
   * @return true if range has another page, false if not.
   */
  public boolean nextPage() {
    if (toIndex >= values) {
      return false;
    }

    if (toIndex > 0) // Not first invocation
    {
      fromIndex += pageSize;
    }

    toIndex = Math.min((fromIndex + pageSize), values);

    return true;
  }

  /**
   * Returns the number of pages in the list.
   *
   * @return number of pages.
   */
  public int pageCount() {
    int r = values / pageSize;
    int m = values % pageSize;

    return m == 0 ? r : (r + 1);
  }

  /** Sets the current page position to the first page. */
  public void reset() {
    fromIndex = 0;
    toIndex = 0;
  }

  /**
   * Returns the current from index, which is closed / inclusive.
   *
   * @return the current from index.
   */
  public int getFromIndex() {
    return fromIndex;
  }

  /**
   * Returns the current to index, which is open / exclusive.
   *
   * @return the current to index.
   */
  public int getToIndex() {
    if (toIndex == 0) {
      throw new IllegalStateException("nextPage() must be called before getToIndex()");
    }

    return toIndex;
  }

  /**
   * Returns the page size.
   *
   * @return the page size.
   */
  public int getPageSize() {
    return pageSize;
  }

  /**
   * Returns a list of all pages. Each item is an array where index 0 holds the from index and index
   * 1 holds the to index. Resets the page.
   *
   * @return a list of all pages.
   */
  public List<int[]> getPages() {
    List<int[]> pages = new ArrayList<>();

    while (nextPage()) {
      int[] range = {getFromIndex(), getToIndex()};
      pages.add(range);
    }

    reset();

    return pages;
  }
}
